feat(sidebar): show update time instead of creation time

apps/web/src/components/ChatView.logic.ts

@@ -28,6 +28,7 @@ export function buildLocalDraftThread(
     messages: [],
     error,
     createdAt: draftThread.createdAt,
+    updatedAt: draftThread.createdAt,
     latestTurn: null,
     lastVisitedAt: draftThread.createdAt,
     branch: draftThread.branch,

apps/web/src/components/Sidebar.logic.test.ts

@@ -1,12 +1,18 @@
 import { describe, expect, it } from "vitest";
 
 import {
+  compareThreadsByLastActivity,
   hasUnseenCompletion,
   resolveSidebarNewThreadEnvMode,
   resolveThreadRowClassName,
   resolveThreadStatusPill,
   shouldClearThreadSelectionOnMouseDown,
 } from "./Sidebar.logic";
+import { ThreadId } from "@t3tools/contracts";
+
+function makeThreadId(id: string): ThreadId {
+  return ThreadId.makeUnsafe(id);
+}
 
 function makeLatestTurn(overrides?: {
   completedAt?: string | null;
@@ -176,6 +182,55 @@ describe("resolveThreadStatusPill", () => {
   });
 });
 
+describe("compareThreadsByLastActivity", () => {
+  it("sorts by updatedAt when present, newest first", () => {
+    const older = {
+      id: makeThreadId("thread-old"),
+      createdAt: "2026-03-01T10:00:00.000Z",
+      updatedAt: "2026-03-01T12:00:00.000Z",
+    };
+    const newer = {
+      id: makeThreadId("thread-new"),
+      createdAt: "2026-03-01T10:00:00.000Z",
+      updatedAt: "2026-03-01T14:00:00.000Z",
+    };
+    expect(compareThreadsByLastActivity(older, newer)).toBeGreaterThan(0);
+    expect(compareThreadsByLastActivity(newer, older)).toBeLessThan(0);
+  });
+
+  it("falls back to createdAt when updatedAt is absent", () => {
+    const older = { id: makeThreadId("thread-a"), createdAt: "2026-03-01T10:00:00.000Z" };
+    const newer = { id: makeThreadId("thread-b"), createdAt: "2026-03-01T12:00:00.000Z" };
+    expect(compareThreadsByLastActivity(older, newer)).toBeGreaterThan(0);
+    expect(compareThreadsByLastActivity(newer, older)).toBeLessThan(0);
+  });
+
+  it("uses id as tiebreaker when timestamps are equal", () => {
+    const a = {
+      id: makeThreadId("thread-aaa"),
+      createdAt: "2026-03-01T10:00:00.000Z",
+      updatedAt: "2026-03-01T10:00:00.000Z",
+    };
+    const b = {
+      id: makeThreadId("thread-zzz"),
+      createdAt: "2026-03-01T10:00:00.000Z",
+      updatedAt: "2026-03-01T10:00:00.000Z",
+    };
+    expect(compareThreadsByLastActivity(a, b)).toBeGreaterThan(0);
+    expect(compareThreadsByLastActivity(b, a)).toBeLessThan(0);
+  });
+
+  it("produces stable sort order for array", () => {
+    const threads = [
+      { id: makeThreadId("thread-1"), createdAt: "2026-03-01T10:00:00.000Z", updatedAt: "2026-03-01T14:00:00.000Z" },
+      { id: makeThreadId("thread-2"), createdAt: "2026-03-01T10:00:00.000Z", updatedAt: "2026-03-01T12:00:00.000Z" },
+      { id: makeThreadId("thread-3"), createdAt: "2026-03-01T10:00:00.000Z", updatedAt: "2026-03-01T16:00:00.000Z" },
+    ];
+    const sorted = [...threads].toSorted(compareThreadsByLastActivity);
+    expect(sorted.map((t) => t.id)).toEqual(["thread-3", "thread-1", "thread-2"]);
+  });
+});
+
 describe("resolveThreadRowClassName", () => {
   it("uses the darker selected palette when a thread is both selected and active", () => {
     const className = resolveThreadRowClassName({ isActive: true, isSelected: true });

apps/web/src/components/Sidebar.logic.ts

@@ -5,6 +5,27 @@ import { findLatestProposedPlan, isLatestTurnSettled } from "../session-logic";
 export const THREAD_SELECTION_SAFE_SELECTOR = "[data-thread-item], [data-thread-selection-safe]";
 export type SidebarNewThreadEnvMode = "local" | "worktree";
 
+export type ThreadSortInput = Pick<Thread, "id"> & {
+  createdAt: string;
+  updatedAt?: string;
+};
+
+/**
+ * Comparator for sorting threads by last activity (updatedAt, then createdAt), newest first.
+ * Uses thread id as tiebreaker for deterministic order.
+ */
+export function compareThreadsByLastActivity(
+  a: ThreadSortInput,
+  b: ThreadSortInput,
+): number {
+
+  const byDate =
+    new Date(b.updatedAt ?? b.createdAt).getTime() -
+    new Date(a.updatedAt ?? a.createdAt).getTime();
+  if (byDate !== 0) return byDate;
+  return b.id.localeCompare(a.id);
+}
+
 export interface ThreadStatusPill {
   label:
     | "Working"

apps/web/src/components/Sidebar.tsx

@@ -84,6 +84,7 @@ import { useThreadSelectionStore } from "../threadSelectionStore";
 import { formatWorktreePathForDisplay, getOrphanedWorktreePathForThread } from "../worktreeCleanup";
 import { isNonEmpty as isNonEmptyString } from "effect/String";
 import {
+  compareThreadsByLastActivity,
   resolveSidebarNewThreadEnvMode,
   resolveThreadRowClassName,
   resolveThreadStatusPill,
@@ -385,11 +386,7 @@ export default function Sidebar() {
     (projectId: ProjectId) => {
       const latestThread = threads
         .filter((thread) => thread.projectId === projectId)
-        .toSorted((a, b) => {
-          const byDate = new Date(b.createdAt).getTime() - new Date(a.createdAt).getTime();
-          if (byDate !== 0) return byDate;
-          return b.id.localeCompare(a.id);
-        })[0];
+        .toSorted(compareThreadsByLastActivity)[0];
       if (!latestThread) return;
 
       void navigate({
@@ -1295,12 +1292,7 @@ export default function Sidebar() {
                 {projects.map((project) => {
                   const projectThreads = threads
                     .filter((thread) => thread.projectId === project.id)
-                    .toSorted((a, b) => {
-                      const byDate =
-                        new Date(b.createdAt).getTime() - new Date(a.createdAt).getTime();
-                      if (byDate !== 0) return byDate;
-                      return b.id.localeCompare(a.id);
-                    });
+                    .toSorted(compareThreadsByLastActivity);
                   const isThreadListExpanded = expandedThreadListsByProject.has(project.id);
                   const hasHiddenThreads = projectThreads.length > THREAD_PREVIEW_LIMIT;
                   const visibleThreads =
@@ -1551,7 +1543,9 @@ export default function Sidebar() {
                                               : "text-muted-foreground/40"
                                           }`}
                                         >
-                                          {formatRelativeTime(thread.createdAt)}
+                                          {formatRelativeTime(
+                                            thread.updatedAt ?? thread.createdAt,
+                                          )}
                                         </span>
                                       </div>
                                     </SidebarMenuSubButton>

apps/web/src/store.test.ts

@@ -26,6 +26,7 @@ function makeThread(overrides: Partial<Thread> = {}): Thread {
     proposedPlans: [],
     error: null,
     createdAt: "2026-02-13T00:00:00.000Z",
+    updatedAt: "2026-02-13T00:00:00.000Z",
     latestTurn: null,
     branch: null,
     worktreePath: null,

apps/web/src/store.ts

@@ -309,6 +309,7 @@ export function syncServerReadModel(state: AppState, readModel: OrchestrationRea
         })),
         error: thread.session?.lastError ?? null,
         createdAt: thread.createdAt,
+        updatedAt: thread.updatedAt,
         latestTurn: thread.latestTurn,
         lastVisitedAt: existing?.lastVisitedAt ?? thread.updatedAt,
         branch: thread.branch,

apps/web/src/types.ts

@@ -96,6 +96,7 @@ export interface Thread {
   proposedPlans: ProposedPlan[];
   error: string | null;
   createdAt: string;
+  updatedAt: string;
   latestTurn: OrchestrationLatestTurn | null;
   lastVisitedAt?: string | undefined;
   branch: string | null;

apps/web/src/worktreeCleanup.test.ts

@@ -20,6 +20,7 @@ function makeThread(overrides: Partial<Thread> = {}): Thread {
     proposedPlans: [],
     error: null,
     createdAt: "2026-02-13T00:00:00.000Z",
+    updatedAt: "2026-02-13T00:00:00.000Z",
     latestTurn: null,
     branch: null,
     worktreePath: null,